HVAC controller area network hybrid network topology

ABSTRACT

The present disclosure provides a CAN network topology for an HVAC communication system. The CAN network topology comprises at least three primary nodes having a predetermined termination impedance and a plurality of end nodes coupled to each primary node, wherein the predetermined termination impedance is set to the optimal setting of 180 ohms. Advantageously, the present disclosure eliminates the need for physically setting CAN node terminations. This reduces install time and removes variability of the install settings. Further, removing this variability reduces the risk for post-installation call-backs due to incorrect system setup. The present disclosure optimizes signal slew rate, which improves signal reliability.

BACKGROUND 1. Technical Field

The present disclosure generally relates to communication systems, andmore particularly, to a Controller Area Network (CAN) hybrid networktopology for a heating, ventilation, and air conditioning (HVAC)communication system.

2. Background of Related Art

The Controller Area Network (CAN) network protocol providesdeterministic communication in complex distributed systems and providesseveral advantages, such as the ability to assign priority to messagesand guarantee maximum latency times, multicast communication withbit-oriented synchronization, system wide data consistency, multiplemaster access to the bus, error detection and signaling with automaticretransmission of corrupted messages, and detection of possiblepermanent failures of nodes and automatic deactivation of defectivenodes. Even though a CAN network offers a number of advantages, a commonconcern is manual electrical termination of network nodes.

Since CAN signals are propagated on a common bus, reflected signalscompromise the integrity of the system. For a node to read the bus levelcorrectly it is important that signal reflections be avoided. This isdone by terminating the bus line with a termination resistor at bothends of the bus and by avoiding unnecessarily long stub lines of thebus. The highest possible product of transmission rate and bus lengthline may be achieved by keeping as close as possible to a single linestructure and by terminating both ends of the line. However, the methodof terminating CAN hardware can vary depending on the physical layer ofthe hardware. Incorrectly terminated configurations lead to decreasedsignal quality, especially in field scenarios. Further, addingadditional communicating devices to the network often requires thetermination resistors be changed.

A CAN HVAC Hybrid Network Topology that eliminates the need forphysically setting CAN node terminations and reduces installation timeand removes variability of installation settings would be a welcomeadvance.

SUMMARY

The present disclosure discloses a CAN network topology for a HVACcommunication system. The present disclosure provides a terminationimpedance for high speed communications at three primary nodes of aphysically distributed system, e.g. an HVAC system, such that additionalcommunicating devices and products may be added to the network withoutchanging the termination resistors and without material detriment to thesignal quality and therefore data throughput of the network.

The CAN network topology comprises at least three primary nodes having apredetermined termination impedance and a plurality of end nodes coupledto each primary node, wherein the predetermined termination impedance isset to the optimal setting of 180 ohms. In another embodiment, thedisclosure provides a method for manufacturing a component for the HVACsystem. In one embodiment, the method includes: providing at least threeprimary hubs or nodes; and setting a predetermined termination level ateach primary hub.

In another embodiment, a method for providing a CAN Network Topology isdisclosed. The method comprises a step of determining at least threeprimary hubs suitable for installing one or more end nodes. The methodfurther comprises a step providing a predetermined termination level ateach primary hub. The method further comprises a step installing one ormore end nodes without the need for physically setting nodeterminations. The method further comprises a step of enhancing signalintegrity by optimizing rise and fall times of the end nodes via thepredetermined termination level.

Other objects, features and advantages of the present disclosure willbecome apparent from the following detailed description. It should beunderstood, however, that the detailed description and the specificexamples, while indicating specific embodiments of the disclosure, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the disclosure will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein will be better understood from the followingdetailed description with reference to the drawings, in which:

FIG. 1 illustrates a CAN network configuration according to an exemplaryembodiment of the present disclosure;

FIG. 2 illustrates a high-level block diagram of a HVAC systemconstructed according to an exemplary embodiment of the presentdisclosure;

FIG. 3 illustrates a transceiver circuit according to an exemplaryembodiment of the present disclosure;

FIG. 4 illustrates a high-level block diagram of a HVAC communicationsnetwork constructed according to an exemplary embodiment of the presentdisclosure;

FIG. 5 illustrates a flowchart for providing a CAN Network Topologyaccording to an embodiment of the present disclosure; and

FIGS. 6A-6D illustrate a wiring diagram of a HVAC system according to anexemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

A description of embodiments of the present disclosure will now be givenwith reference to the Figures. It is expected that the presentdisclosure may be embodied in other specific forms without departingfrom its spirit or essential characteristics. The described embodimentsare to be considered in all respects only as illustrative and notrestrictive. The scope of the disclosure is, therefore, indicated by theappended claims rather than by the foregoing description. All changesthat come within the meaning and range of equivalency of the claims areto be embraced within their scope. The words “exemplary” and“exemplarily” are used herein to mean “serving as an example, instance,or illustration.” Any embodiment described herein as “exemplary” is notnecessarily to be construed as preferred or advantageous over otherembodiments. The word “example” may be used interchangeably with theterm “exemplary.” The term “effective” or “effectively” includes targetor nominal values within reasonable engineering tolerances that canachieve a desired technical objective.

Disclosed herein is a communications network that is designed to providea universal plug and play termination scheme that preserves the qualityof signals transmitted across the network. As such, technicians do nothave to be relied upon to provide matching impedances for communicationsnetworks. Instead, the disclosure provides a physical network withpredetermined termination levels at three primary hubs of the network topreserve signal quality. Accordingly, components can be manufacturedhaving these predetermined termination impedances to provide a plug andplay solution. For example, the predetermined termination impedance maybe embedded in electronic controllers at three primary hubs of thecommunications networks. The controllers may be computing devicesdesigned to direct the operation of a particular component at each node.Interface circuitry of the controllers may include the predeterminedtermination impedance at three primary nodes of the communicationsnetworks. The interface circuitry may include a transceiver of theelectronic controllers and a physical interface circuitry for thetransceiver.

Advantageously, the communications length between multiple nodes of thedisclosed communications network can vary without affecting signalquality. As such, the disclosed network can be used for HVAC systemsthat have various configurations due to the requirements of individualinstallation sites. Accordingly, the disclosed communications networkcan compensate for variable communication lengths between the coupledcomponents. Additionally, the disclosed communications network cancompensate for different wire sizes used for interconnecting nodes ofthe network. As such, the provided communications network is wiresize-agnostic.

FIG. 1 illustrates a network topology diagram 100 of an embodiment of aCAN network constructed according to the principles of the presentdisclosure. The network topology diagram provides a layout ofinterconnections of the various elements (e.g., nodes) of the CANnetwork. The CAN network may be a communications network within astructure. For example, the CAN network may be a building automationcommunications network (BACNet) that provides a medium forcommunications within one or more buildings between coupled componentsof the communications network.

The CAN network comprises at least three primary nodes 102 and aplurality of end nodes 104. In one embodiment, the CAN network may be acommunications network for an HVAC system. As such, the at least threeprimary nodes 102 and the plurality of end nodes 104 may be thecomponents of the HVAC system.

Each of the primary nodes 102 includes a transceiver circuit having asimilar effective termination impedance. More specifically, theterminations of each of the three primary nodes 102 is set to 180 ohms.In one embodiment, the primary node 102 and the plurality of end nodes104 may be electronic controllers of each component at the particularnodes. As such, the transceiver circuit of each node may be thetransceiver circuit of the electronic controllers.

The primary node 102 is coupled to each of the plurality of end nodes104 by one of a network interconnect or interconnection 106 to form aphysical network topology. The interconnections 106 provide adifferential communication bus between nodes (102, 104) of the CANnetwork. The primary node 102 has usually the highest number ofinterconnections 106 connected to it. In one embodiment, theinterconnections 106 may be copper wire.

The CAN network comprises a physical hybrid topology of star and mesh.The primary node 102 is established as a control node for the CANnetwork and has a predetermined impedance. The predetermined impedancemay also be embedded in an electronic controller at the primary node102. In one embodiment, the predetermined impedance has a resistancewithin a range of 50 ohms to 200 ohms. The predetermined impedance canallow various wire sizes to be used for the interconnections 106. Assuch, the communications network is a wire size-agnostic network.

In one embodiment, the predetermined impedance is based upon, at leastin part, a characteristic of a transceiver at the primary node 102. Thecharacteristic may be an operating parameter of the transceiver. Thecharacteristic may be a current limit, a voltage limit, a capacitancelimit or a DC load limit for the transceiver. The transceiver may be aBosch Controller Area Network (CAN) compliant transceiver. The CANtransceiver may comply with various CAN specifications, includingrevision 2 or ISO-11898. In another embodiment, the transceiver may bean RS-485 compliant transceiver. The RS-485 transceiver may comply withvarious versions of transceivers for an RS-485 network. Withpredetermined impedances, the CAN network preserves the quality ofsignals traversing thereon and substantially reduces or eliminatesreflections at the connections of the interconnections 106 with theprimary node 102 and the plurality of end nodes 104.

The three predetermined termination points and impedance values areconfigured to provide enhanced signal integrity by optimizing rise andfall times for a variety of user configurations. Also, thisconfiguration eliminates the need for switches, relays, or other meansof configuring nodes. In another embodiment, the disclosure provides amethod for manufacturing a component for the HVAC system. In oneembodiment, the method includes providing at least three primary hubsand setting a predetermined termination level at each primary hub.

FIG. 2 illustrates a high-level block diagram of an exemplary HVACsystem 200 constructed in accordance with the present disclosure. TheHVAC system 200 includes a communications network as discussed withrespect to FIG. 1. As such, the HVAC system 200 includes acommunications network 260 that couples together the various componentsof the HVAC system 200.

The HVAC system 200 includes an air handler 210 that is configured tocondition and circulate air for the HVAC system 200. The air handler 210may include heating and/or cooling elements to condition air, and ablower to move the air through the HVAC system 200 and into anenclosure. As such, the air handler 210 may include a furnace and orevaporator coils. Additionally, the air handler 210 may be associatedwith an outdoor unit 220. Typically, the air handler 210 is an indoorunit. The outdoor unit 220 may include a compressor 222 and associatedcondenser coils 224 that are typically connected to an associatedevaporator coil in the air handler 210 by a refrigerant line 226. Oneskilled in the art will understand that the HVAC system 200 may includemultiple air handlers and, therefore, include multiple associatedcomponents as indicated in FIG. 2. Descriptions of FIG. 2, however, willonly refer to one of the components. Additionally, one skilled in theart will understand that the HVAC system 200 may include additionalcomponents, such as dampers, a thermostat, heat recovery ventilator(HRV), energy recovery ventilator (ERV), and so forth, that are notillustrated or discussed but may be included in an HVAC system.

A control unit 230 controls the air handler 210 and/or the compressors222 to regulate the temperature of the premises. The display 240 canprovide additional functions such as operational, diagnostic and statusmessage displays and a visual interface that allows a technician toperform actions with respect to the HVAC system 200 more intuitively.

A comfort sensor 250 may be associated with the display 240 and may alsooptionally be associated with the control unit 230. The comfort sensor250 provides environmental data, e.g. temperature, humidity, and/orbarometric pressure, to the control unit 230. The comfort sensor 250 maybe physically located within a same enclosure or housing as the controlunit 230, in a manner analogous with a conventional HVAC thermostat. Inthat case, the comfort sensor 250 and the control unit 230 may share thesame transceiver circuit. In other embodiments, the comfort sensor 250may be located separately and physically remote from the control unit230.

The HVAC system 200 also includes communications network 260 that isconfigured to provide a communication medium between or among theaforementioned components of the HVAC system 200. Accordingly, thecommunications network 260 couples the air handler 210, the outdoor unit220, the control unit 230, the display 240 and the remote comfort sensor250 such that data may be communicated therebetween or there among. Thedata may be control data. Additionally, the communications network 260may be advantageously employed to convey one or more alarm messages orone or more diagnostic messages. Each of the components of the HVACsystem 200 includes a transceiver that is configured to communicate(transmit and receive) data over the communications network 260. Thattransceiver, together with other associated components comprises thetransceiver circuit.

The communications network 260 includes interconnections 262 and thevarious transceiver circuits 264, 265, 266, 267 and 268. Thecommunications network 260 is a CAN network as discussed with respect toFIG. 1. One of the components, or more specifically, one of thetransceiver circuits thereof, may be designated as the primary node. Forexample, the transceiver circuit 264 may be designated as the primarynode. The other transceiver circuits 265, 266, 267 and 268, maytherefore be designated as end nodes.

At least some of the transceiver circuits of the communications network260 may be part of a local controller (not illustrated) for eachparticular component. Local controllers are electronic controllers thatmay be configured to provide a physical interface for the communicationsnetwork 260 and provide various functions related to networkcommunication. A representative controller for each component of theHVAC system 200 is illustrated in FIG. 3. The controller 230 may beregarded as a special case of an electronic controller, in which thecontroller 230 has additional functionality enabling it to controloperation of the various networked components, to manage aspects ofcommunication among the networked components, or to arbitrateconflicting requests for network services among these components.

Turning now to FIG. 3, a transceiver circuit with predeterminedtermination impedance is disclosed. The transceiver circuit includes aRS-485 transceiver 300 having a device controller 301. The devicecontroller 301 includes a processor, memory, interface circuitry, andoperating software to monitor and control the operation of HVAC systemor device 302. The operating software may be embodied in a set ofinstructions stored in the memory and executable on the processor.Device controller 301 is communicatively coupled via controller signallines 307 to CAN bus interface 303 which provides an interface betweendevice controller 301 and CAN bus signal lines 311 to communicate BASdata between network media 208 and device controller 201 using the CANbus protocol. CAN bus interface 303 may be an integrated circuit (IC)such as, without limitation, a “TJA1042 High-Speed CAN Transceiver withStandby Mode” manufactured by NXP Semiconductors N.V. of Eindhoven, TheNetherlands. CAN bus signal lines 311 include CAN high line 311 a andCAN low line 311 b in a balanced pair configuration. Protection circuit309 is interposed between CAN bus signal lines 311 and CAN bus network308 and includes overcurrent limiting devices 312 and overvoltagelimiting devices 313 to protect RS-485 transceiver 300 from harmfulelectrical transients which may occur on CAN bus network 308.

In the present exemplary embodiment, overcurrent limiting device 312include a pair of positive temperature coefficient (PTC) thermistorscoupled in series, respectively, on each leg of CAN bus signal lines 311between CAN bus network 308 and CAN bus interface 303. Overcurrentlimiting device 312 may additionally or alternatively include a fuse,fusible link, circuit breaker, or other suitable current protectioncircuit. Overvoltage limiting device 312 may include a Zener diodeconfigured to shunt CAN bus signal line 311 to ground during anovervoltage condition. In some embodiments, overvoltage limiting device312 may additionally or alternatively include a metal oxide varistor(MOV) or other suitable voltage protection circuit. A connector 304,such as a terminal block or other electrical connector couples RS-485transceiver 300 to CAN bus network 308.

RS-485 transceiver 300 includes a termination resistor circuit 310having a termination resistor 306. Termination resistor 306 may beselectively coupled to the CAN bus, e.g., between CAN high line 311 aand CAN low line 311 b, via electronic switch 330. In the presentembodiment, termination resistor 306 has a value of 180Ω, however, thepresent disclosure is not so limited and therefore termination resistor306 may have any desired value. In another embodiment, the terminationresistor 306 has a value of 50 ohms to 200 ohms.

FIG. 4 illustrates a high-level block diagram of an embodiment of a HVACcommunications network 400 constructed according to the principles ofthe disclosure. The network 400 includes multiple nodes coupled togethervia interconnections 450. The interconnections may be formed from copperwire. For example, the interconnections 450 may be a 4-wire cable. Thenodes of the communications network 400 may be controllers (notexplicitly shown) of the various illustrated components. The controllersmay include transceiver circuits to direct communications via thecommunications network 400 and provide terminations for theinterconnections 450. One of the components, or a controller thereof,may be designated a primary node wherein the remaining components areend nodes. The components include a controller 410, a user interface420, a comfort sensor 430 and a furnace 440 configured to communicateover the interconnections 450. In some embodiments these devices form aminimal HVAC network. In addition, the network 400 is illustrated asconnecting an outdoor unit 460, an outdoor sensor 470, and a gateway480. The transceiver of each of these components may be coupled to theinterconnections 450 to form the communications network 400.

The controller 410 is configured to control the furnace 440 and theoutdoor unit 460 using command messages sent via the interconnections450. The controller 410 may receive environmental data, includingtemperature, relative humidity and/or barometric pressure, from thecomfort sensor 430, the furnace 440, the outdoor sensor 470 and/or theoutdoor unit 460. The data may be transmitted over communicationsnetwork 400 by way of messages formatted for this purpose. The userinterface 420 may include a display and input means to communicateinformation to, and accept input from, an operator or manager of thenetwork 400. The display and input means may be a touch-sensitivedisplay screen.

The controller 410, comfort sensor 430 and user interface 420 mayoptionally be physically located within a control unit 490. The controlunit 490 provides a convenient terminal to the operator to effectoperator control of the system. In this sense, the control unit issimilar to the thermostat used in conventional HVAC systems. However,the control unit 490 may only include the user interface 420, with thecontroller 410 and comfort sensor 430 remotely located from the controlunit 490.

The controller 410 may control HVAC functionality, store configurations,and assign addresses during system auto configuration. The userinterface 420 provides a communication interface to provide informationto and receive commands from a user. The comfort sensor 430 may measureone or more environmental attributes that affect user comfort, e.g.,ambient temperature, relative humidity, and barometric pressure. Thethree logical devices 410, 420, 430 each send and receive messages overthe communications network 400 to other devices attached thereto, andhave their own addresses on the network 400.

FIG. 5 illustrates an exemplary method 500 for providing a CAN NetworkTopology according to an embodiment of the present disclosure. Themethod 500 comprises a step 502 of determining at least three primaryhubs suitable for installing one or more end nodes. The method 500comprises a step 504 providing a predetermined termination level at eachprimary hub. The method 500 comprises a step 506 installing one or moreend nodes without the need for physically setting node terminations. Themethod 500 comprises a step 508 of enhancing signal integrity byoptimizing rise and fall times of the end nodes via the predeterminedtermination level.

As the majority of installations have three essential pieces ofequipment including an outdoor unit, an indoor unit and a thermostat,the present disclosure utilizes at least three primary nodes. Theoutdoor unit may include an A/C condensing unit or a heat pump unitproviding condensing operation in cooling (A/C) mode and evaporatingoperation in heating mode. The indoor unit may include an A/Cevaporating unit or a dual- or tri-mode air handler that providesevaporating in cooling mode, condensing in heating mode, and/orconcurrent evaporating and condensing in dehumidification mode. Thethermostat may include a smart thermostat with graphic user interface(UI), and a UI control panel used with one or more environmental sensors(e.g., temperature, relative humidity, barometric pressure, and thelike).

Each primary end node comprises a 180Ω termination impedance, whichprovides acceptable reduction of reflections (e.g., voltage standingwave ratio or “VSWR”) when used in the disclosed star configuration withsecondary endpoint nodes. This eliminates the need for an installationtechnician to have the skill, or spend the time, to adjust terminationsettings in each node, as practiced in the prior art. Consistency andreliability are improved, and fault detection and diagnosis issimplified since the variable termination permutations of prior artsystems is removed from the disclosed system. Manufacturing costs arealso reduced since termination resistors are pre-set in the primarynodes, thereby eliminating the need for DIP switches or otherconfiguration means, nor for termination resistors in the secondarynodes.

Examples of secondary endpoint (non-terminated) equipment suitable foruse with the disclosure, include, but not limited to, temperature and/orhumidity sensors, dampers, zoning kits, user interface panels, networkbridges (to access internet, cloud, mobile app), air cleaners(electrostatic), humidifiers, dehumidifiers, heat recovery ventilators(HRV), energy (or enthalpy) recovery ventilators (ERV), fuel levelsensors, weather sensors, demand-response interface and backup powerinterface.

FIG. 6A-6D illustrates a wiring diagram of an exemplary HVAC system 600constructed according to an embodiment of the present disclosure. TheHVAC system 600 includes a distributor hub 616 that couples the variouscomponents of the HVAC system 600. The distributor hub 616 is connectedto a plurality of network devices including at least three primary nodesand one or more secondary end nodes 630 via one or more network cables620. Each primary end node comprises 180Ω termination resistor 614,which provides acceptable reduction of reflections (VSWR) when used in astar configuration with endpoint of secondary node 630. The distributorhub 616 is also connected to an end node user interface 622. The endnode user interface 622 could be a display or touch screen. At leastthree primary nodes include an indoor unit such as an air handler 602,an outdoor unit and a wireless interface 624, and the secondary node 630could be a damper, zoning kit and air cleaner. The air handler 602 isconfigured to condition and circulate air and may include heating and/orcooling elements.

The HVAC system 600 may include non-network devices such as a powertransformer or indoor transformer (XFMR) 604, pressure sensor, staticpressure sensor 606, electric heat relay panel 608, blower or variablespeed (VSPD) motor 610. Additionally, HVAC system 600 includescommunication (COMM) and status (STATUS) indicators 612 and spareconnectors 618. The air handler 602 is associated with the outdoor unit.The outdoor unit includes a compressor drive 632 and associatedcondenser coils that are typically connected to an associated evaporatorcoil in the air handler 602 by a refrigerant line. A control unit 634controls the air handler 602 and/or the compressor drive 632 to regulatethe temperature of the premises. The HVAC system 600 further compriseswireless interface 624 to provide a communication medium between thecomponents of HVAC system 600 or the user device such as router 626,mobile device 628 associated with the user. Mobile device 628 mayinclude a mobile application component installed thereon. In oneembodiment, the wireless interface 624 may be a Wi-Fi, Z-Wave,Bluetooth, Bluetooth Low Energy (BLE), or Zigbee wireless interface.

Advantageously, the present disclosure eliminates the need for atechnician to set or adjust CAN node terminations. This reducesinstallation time and removes variability from the installationsettings. Removing this variability may in turn reduce the likelihood ofpost-installation call-backs due to incorrect system setup. The presentdisclosure optimizes signal slew rate, which improves signalreliability. This present disclosure provides a best compromise for awide range installation scenarios expected in HVAC systems. The additionof new accessories (nodes) requires no additional termination orconfiguration under the principles of the present disclosure.

Particular embodiments of the present disclosure have been describedherein, however, it is to be understood that the disclosed embodimentsare merely examples of the disclosure, which may be embodied in variousforms. Well-known functions or constructions are not described in detailto avoid obscuring the present disclosure in unnecessary detail.Therefore, specific structural and functional details disclosed hereinare not to be interpreted as limiting, but merely as a basis for theclaims and as a representative basis for teaching one skilled in the artto variously employ the present disclosure in any appropriately detailedstructure.

What is claimed is:
 1. A controller area network (CAN) topology for acommunication network, comprising: at least three primary nodes having apredetermined termination impedance, and one or more end nodes each ofwhich is coupled to one of the primary nodes, wherein the one or moreend nodes are non-terminated.
 2. The CAN topology of claim 1, whereinthe predetermined termination impedance of each primary node comprises asimilar predetermined termination impedance.
 3. The CAN topology ofclaim 1, wherein the predetermined termination impedance has aresistance of 180 ohms.
 4. The CAN topology of claim 1, wherein thepredetermined termination impedance has a resistance within a range of50 ohms to 200 ohms.
 5. The CAN topology of claim 1, wherein thecommunicating network forms a building communication network.
 6. The CANtopology of claim 1, wherein the communicating network is a heating,ventilation, and air conditioning (HVAC) communications and controlnetwork, wherein the primary nodes and the plurality of end nodes eachinclude an HVAC component.
 7. The CAN topology of claim 1, furthercomprising a hybrid of star configuration and mesh configuration.
 8. TheCAN topology of claim 1, wherein any of the at least three primary nodesis selected from the group consisting of an outdoor unit controller, anindoor unit controller, a thermostat, and a system controller.
 9. Amethod for providing a controller area network (CAN) topology of acommunication network, comprising the steps of: providing at least threeprimary nodes; providing a component having a predetermined terminationresistance at each primary node; and providing an end node coupled to atleast one of the primary nodes, wherein the end node is non-terminated.10. The method of claim 9, wherein each primary node comprises a similartermination impedance.
 11. The method of claim 9, wherein thepredetermined termination impedance has a resistance of 180 ohms. 12.The method of claim 9, wherein the predetermined termination impedancehas a resistance within a range of 50 ohms to 200 ohms.
 13. The methodof claim 9, wherein the communicating network includes a buildingcommunication network.